The present specification relates to a semiconductor device and to a method of making a semiconductor device.
In recent years, GaN/AlGaN High Electron Mobility Transistors (HEMTs) and GaN/AlGaN Schottky diodes have drawn a lot of attention regarding their potential to replace Si or SiC for use as high voltage (HV) devices.
A GaN/AlGaN HEMT typically includes a substrate having an AlGaN layer located on a number of GaN layers. A gate, source and drain are located above the AlGaN layer. During operation, current flows between drain and source via a two-dimensional electron gas (2DEG) that is formed at the interface between the AlGaN layer and an upper GaN layer. Switch-off is achieved by applying a suitable voltage to the gate, such that the 2DEG at the interface between the AlGaN layer and the uppermost GaN layer disappears. The gate may be a Schottky contact or may comprise a gate electrode that is isolated by a dielectric layer (such devices are referred to as Metal Insulator Semiconductor High Electron Mobility Transistors (MISHEMTs).
A GaN/AlGaN Schottky diodes may be similarly constructed, but with two contacts (including a Schottky contact forming an anode and an ohmic contact forming a cathode of the device) instead of three.
Both the HEMT and the Schottky diode suffer from the problem that the on-state resistance under dynamic (e.g. switching, pulsed, RF) conditions may be significantly higher than under DC conditions.